Process of cracking hydrocarbon oils under pressure



Man 20, 1923 EQQZZK H. W.` HANNA ET AL.

PROCESS 0F CRACKING HYDRCARBON OILS UNDER PRESSURE.

FILED SEPLZO, 1921.

Patented Mai. 2(0), i923,

omTsn sTaTes atraen PATENT orales.,

RICHARD W. HANNA, WILLIAM D. MASON, AND WALTER G. HAMILTON, OF RICH- MOND, CALIFORNIA, ASSIGNORS TO STANDARD OIL COMPANY, OE SAN FRANCISCO, CALIFORNIA, A CORPORATION O31" CALIFORNIA.

PROCESS OF CRACKING HYDROCARBON OILS UNDER PRESSURE.

Application filed September 20, 1921. Serial No. 502,031.

T 0 all whom it ymay concern.'

Be it known that We, RICHARD W. HANN-A, lVILLIAM D. MAsoN, and WALTER Gr. HAMIL- TON, residents of Richmond, in the county of Contra Costa, State of California, citizensr of the United States of America, have invented an Improved Process of Cracking Hydrocarbon Oils Under Pressure, of Which the following is a specification.

This invention relates to the decomposing or cracking of hydrocarbon oil to produce a lower boiling point oil from a relatively higher boiling point oil or fraction.

In the cracking of petroleum oil it has heretofore been the practice either (l) to introduce the oil to be treated cold into a still and then by the application ofA heat to A producing an excessive amount of fixed gas,

excessive polymerization, the production of large percentage of unsaturated hydrocarbons, tar and heavy residues, and result in rapid deterioration of the apparatus, Waste of oil, and the production of a produc-t containing a high percentage of unsaturated hydrocarbons.

7e have discovered that lby continuously maintaining the oil while it is being treated at substantially the temperature of the cracking operation, a much more uniform cracking action can be secured, that the degree of cracking or decomposition can be regulated and controlled substantially as desired to produce the desired product; and that this Will be accompanied With the production of a minimum of' fixed gas, a minimum polymerization of the residual oil or resultant high boiling point residues.l and that a much more uniform product will be produced containing a. minimum of unsaturated hydrocarbons resultant from the cracking. `We secure this result by providing an evaporating chamber in which the oil to be Va circulating means by which a stream of oil is constantly taken from the evaporating chamber and circulated through a heating zone, for instance a heating coil or apparatus, and delivered backinto the body of oil in the vaporizing chamber so that substantially all portions of tlie body of oil being treated are repeatedly circulated from such evaporating chamber to and through the heating Zone and back into the body of oil in the evaporating chamber. By providing such a circulation of the oil from the evaporating chamber through the heating zone and back into the body of oil in the evaporating chamber in such volume or at. such rate of How that the entire body of oil in the apparatus or system is subjected to such reheating at intervals of approximately ten minutes, ive are enabled to maintain the body of oil in the evaporating chamber at a substantially constant temperature ivithout subjecting it at any time to an excessive temperature. This heating vcoil may be. and preferably is, externally heated, so that the oil as it circulates therethrough is slightly raised in temperature, preferably not more than 15 degrees above the temperature to be maintained in the body of 'oil in the evaporating chamber. `We have found this differential in temperature ample to keep the body of oil in the evaporating chamber at a substantially constant temperature. this additional heat being sufficient to compensate for the loss of heat due to vaporization from the vaporizing chamber, loss due to radiation, etc. We have also found that by thus controlling the temperature of the oilkbeing treated We need not pass the oil through a heating Zone or coil heated to such degree as Will'teiid to excessively crack any material part thereof or subject the oil at perature.

We havealso discovered in the cracking"' of a relatively high boiling point oil to produce a relatively low boiling point fraction that Where the oil to be treated is circulated from an evaporating chamber or bulk supply to and through a heating Vzone, chamber or coil the yield of 10W boiling point oil can be materially increased if the pressure on the heating coil or heating zone or chamber is-maintained ten pounds or more in excess of the pressure kept `upon the evaporatiiig chamber or bulk supply. This increase in yield may be accounted for as follows: The oil passing through the heating coil is subjected to decomposing conditions of temperature and pressure and the lighter fractions being subjected to this higher temperature are superheated; a partof them are further decomposed or broken down, forming fixed gas and resultant high boiling point oils or residues, and `are a loss. If an'additional pressure is exerted upon .the oil in the heatin zone, chamber or coil, this action is materia ly prevented; that is to say,

the light fractions are not further reduced due tothe pressure increasing the density of the oil. We have found, therefore, that in a circulating system where the heating zone,

chamber or coil is heated to a temperature five degrees or more in excess of the temperature maintained in the still proper or evaporating chamber such heated oil may readily 'be intermingled with the relatively i cooler oil in the b-ulk supply or evaporating a part o chamberthat such heated oil will give upits heat to the oil in such still or evaporating chamber." Thereby the incoming or extra heated oil-is cooled to a certain degree and this extra pressure can be released without the danger of such light or ing into gas.

relatively low boiling point .fractions breaklf, for example, the pressure upon the oil being treated in the evaporating chamber or bulk supply is siXty to one hundred pounds, then from lten to fifty pounds additional pressure may be maintained upon the oil as it is subjected to the temperature of the heating zone or coil. These pressures will var somewhat with the decomposing or cracking operation being carried on and the character of oils being treated.

In ordinary cracking operations, where j the temperature of the oil being treated and lat the outlet of the heating zone, chamber or y coil is materially higher than that the the oil. in the bulk supply or evaporating chamber,

the larger portion of the cracking is done in the heating zone, chamber or coil proper. This has a tendency to deposit an excessive amount of carbon in the heating chamber or element. We have found that by maintaining all the oil in the systeml at approxi-A .inately the same temperature, or, in`other words, maintaining a low differential temperature between the outlet from the heating element or chamber into the evaporating or bulksupply and the temperature of the oil in such evaporator or bulk supply that all 'or substantially all of the cracking or decomposition takes place in the evaporating chamber or bulk supply andnot in the heating element 'or chamber. Thereby such carby..avoiding all sudden or excessive raises inl temperature which produce excessive deo-il.

While our invention is! not `dependent upon any particular lform or construction of apparatus, it may be more fully and readily composition or cracking of portions of the understood'in connection with a-system and i apparatus by which it may be performed. We have, therefore, shown and illustrated in the accompanying drawings a diagrammatic view of a system or apparatus in which a preferred form of a process embodying our invention may be performed.

'We prefer to originally bring the entire i body of the oil, to be subjected to thel cracking operationto= the required cracking temperature without subjecting any portion thereof to an abrupt or to an excessive raise in temperature, thereby avoiding excessive cracking and to subject all the oil to an even and uniform cracking distillation. To this end we prefer to provide for a primary or preparatory heating of the charging stock before it is introduced into the cracking unit or system. lSuch primary or preparatory heating of the charging stock, however, forms the subject matter of our application filed August 29, 1921, Serial No. 496,403.

In the drawing, l indicates a storage vesduced by cracking such high boiling pointy oil. and preventing such heavy bodies from being so reduced as to. cause depositionl in the system.. Such solvent oil may be any lower boiling point 'fraction of the same oi of which the oil to be cracked is a part, or o f any other oil provided, however, that such solvent oil shall be substantially unaffected at the pressure and temperature employed in the cracking of the particular oil operated upon. It is also understood that the preferred embodiment of our process is not limited to the use of any particular noncrackable or solvent oil either produced in the system or added from any suitable source but may be merely a relatively low boiling point fraction of the oil, cracking of the high boiling point fraction whereof is to be performed. rllhe use of such a solvent oil is incident, however, only to the preferred form and embodiment of our process. 13 indicates a pump adapted to draw solvent oil through the pipe 14 from the vessel 12 and force it through a pipe or conduit 15 into the pipe or conduit 3 Where it is mixed with the oil to be cracked. It is obvious that mixing of the oil to be cracked and solvent oil may take place before the same are supplied to the storage or supply tanks or vessels of the system in which case such mixture may be drawn directly from one tank or vessel and forced through a pipe or conduit 3. From the pipe or conduit 3 this charging stock is forced into and through a Waste hcat exchanger 4; at the condenser 18 and thence through a continuation of such pipe or conduit 3 through a heat exchanger 5, vvhere such charging stock is subjected to the Waste heat of the reflux condenser. From such heat exchanger 5 the conduit 3 is preferably carried to a. Waste heat exchanger 6 at the discharge or Withdrawal of the hot residual solution of the system. From this heat exchanger 6 the charging stock is forced through a continuation of the conduit 3 into and through a heating chamber or zone 7. rlhis heating zone or chamber is indicated in the form of a coil 7 and may be of the ordinary or preferred construction and fired or heated in any preferred manner. By means of this coil the charging stock is brought to the desired teinperature for introduction into the cracking system. Such desired temperature is necessarily higher than any temperature to which the charging stock could be raised by mere Waste heat of vapor heat exchangers. From thel heating unit or coil 7 a pipe or conduit 8 leads into the heating coil or chamber or zone 16 of the cracking system. `While We prefer to introduce. the primarily or preparatorily heated charging stock directly into such heating coil` it may be introducedA at any other desired point in the system.

'lhe cracking apparatus or system proper is indicated as consisting of a suitable vaporizing chamber or evaporator 9. 10 represents a pump connecTing on its suction side by means of a pipe l1 with the vaporizing chamber or evaporator 9 and on its discharge side with a pipe 25 leading to the heating element or coilv 1 6 of the cracking system. 'l` his heating coil or element 16 is preferably mounted in a suitable furnace 26 Where it is either directly or indirectly heated as preferred. rfhe heating coil or elenient 16 is connected by means of a pipe or conduit 27 with the vaporizing chamber or evaporator 9. 27 indicates a suitable valve by means of which a differential pressure may be maintained on the oil in the Vaporizing chamber 9 and heating chamber or coil 16. 2S represents'the vaporxline from the ,dephlegm ator.

lfrom an outside source. of non-orackable or solvent oil passes off.

evaporator 9. 17 represents a dephlegmator or reflux condensing apparatus in said line 28 and 18 is a condenser connected with said 19 indicates a receiver connected with thecondenser and 20 is a valve Where pressure is released and the condensate delivered to storage. 21 is a discharge pipe from the evaporator 9. 22 is a cooler to which the pipe 21 leads throughthe Waste heat exchanger 6. 23 is a discharge valve from the cooler and 24 is a receiver. The pump 2 affords a means by which any desired pressure may be placed and maintained upon the charging stock as it is being primarily heated.

The presence in the charging stock of a fraction of oil of lower boiling point than the oil to be cracked which lower boiling point fraction is substantially unaffected at the temperature and pressure of the cracking operation, provides a medium by which the high boiling point derivatives and heavier bodies lproduced from the cracking of the oil may be carried in solution and be prevented from being reduced so'heavy or so near to tar or carbon as to deposit in the system. ln other Words, this solvent oil immediately takes and holds inl solution the relatively higher boiling point oil or fraction produced by the cracking, so that it may be discharged from the apparatus. -Upon the cracking of the crackable oil into such relatively high and low boiling point fractions, this solvent oil immediately takes into solution and holds such relatively high boiling point derivatives from further reductionto tar or carbon. lf this solvent oil solution is permitted to become overcharged, deposition in the system takes place as these higher boiling point derivatives or fractions, heavy hydrocarbons,tarry Vor carbonaceous bodies take the brunt of the heat, and unless held in solution by the solvent oil become further reduced towards tar or carbon. The degree of concentration, (of the solvent oil and: high boiling point derivatives produced by the cracking of the crackable oil,) Which may be permitted in the system Without danger of deposition will, of course, depend upon the oils 'charged into the system, as, for example, the carbon residue test shouldnot exceed ten times that of the charged oils. This is merely an example and vvill vary With the oils.

ln the cracking of certain petroleum distillates there may be produced from the operation sufficient solvent or non-crackable oil of unsaturated form to keep the higher boiling point derivatives or solid hydrocarbons, tarry residues, etc.` in solution, so that no deposit will form on the metal surface of the heated element, in which case it is unnecessary to add solvent or non-crackable oil A certain amount lll@ - must be heated to higher temperatures in:l

with the higher boiling point derivatives in order to produce and maintain the decomsolution. This may be replaced from storage as needed. I As an example of the proportion of oil to be charged with a solvent oil, we add one volume of the former yto as much as three or five volumes of the latter in the system at any one moment; and as an example .of a desirable cracking pressure and temperature of the oil to be cracked, We give one hundred to one hundred twenty pounds absolute and seven hundred forty-ve de grecs to "eight hundred degrees F. in the evaporating chamber, but it is understood that these proportions and the pressure and temperature may vary according to the oils used and the cracking operation or reaction sought.

While this preferred embodiment of our invention includes this primary or preparatory heating of the fresh charging stock and the use of a solvent oil, the invention is not necessarily limited thereto as either our discovery of the advantageous use of an excess pressure of from ten to fifty pounds over the pressure maintained in the vaporizing chamber, reflux apparatus and condenser,or the temperature control Wherein the temperature of the oil being treated as it is present in any two parts or portions of the system does not differ more than approximately fifteen degree F., or the rapid turnover or subjecting of all the mass or body of oil in the system to the heating chamber or coil at least once in each approxlmately ten minute period-of the operation may be utilized separately. Each of these discoveries we, therefore, claim separately and independently, although we prefer to combine all of them in a single process and thereby secure the maximum efficiency, economy and yields.

Where we do not add more than approximately fifteen degrees F. upon the passage of the oil through the heating zone or coil, we have found it very advantageous to submit the oil on an average of not less than twenty times to such heating zone, depending upon the oil being treated, and sometimes as high as one hundred times before discharge from the system By thus subjecting` the oil to repeated moderate additions of heat to maintain a given substantially constant temperature, we minimize the possibility of excessive cracking or decomposition and produce the maximum amount of the desired product with a minimum formatio-n of high gravity derivatives, the minimum` loss by production of fixed gas and produce in the low boiling point product the minimum unsaturated bodies. If the turnover or subjection of the entire body of oil in the system to the heating zone is not thus maintained, portions of the cracking system posing or cracking reaction.

It is obvious that the temperature of the oil in the heating coil or other heating zone must be relatively'higher than the temperature of the oil in the vaporizing chamber or other portions of the system. If, therefore,

the temperature ofthe oil in the coil be a1- lowed to rise materially beyond that of the bulk oil in the vaporizing chamber, it is evident that vaporization will occur in the coil unless provision is made to prevent this. This vaporization may be prevented by maintaining a certain predetermined pressure on the oil in the heating coil or heating zone in excess of that of the balance of the system, (i. e., vaporizing chamber, condenser, ete).A This differential pressure may be maintained by means of the valve 27 indicated in the drawings or in several other ways, and we do not limit ourselves to any particular means therefor, as, for example, a restricted outlet from the coil to the vaporizer may be used, or by maintaining a suiiiciently rapid flow through the heating coil to cause an appreciable back pressure (velocity head). The latter is preferable,

as it insures a sufliciently rapid flow of oil ing zone and an evaporating chamber, that step which includes maintaining the entire body of. oil in the system lunder the conditions of temperature and pressure of the cracking reaction and'substantially confining the cracking reaction to the evaporatingl chamber, by forcibly circulating the foil from the evaporating chamber to and through the heating zone and back the evaporating chamber at such a relat1on of speed and volume of circulation as to maintain such circulation equal to passing such entire body of oil through the heating zone at intervals of not substantially more than ten minutes whereby such constant temperature and pressure is maintained throughout the system.

2. In a cyclic process of cracking petroleum oil under pressure in a closed system wherein a relatively large body of loil is maintained in the evaporatingfchamber of' the system and a relatively small stream thereof is circulated to and thrbugh a heating zone and back into said chamber, to pro- -duce a substantially uniform cracking reaction in said chamber during the entire run,

that step which consists in maintaining, during the entire run, all portions of such oil at so nearly the same temperature that the temperature o-f the oil at its exit from the heating zone is less than 15 F. above the temperature ofthe oil in said chamber.

3. In a cyclic process of cracking petroleum oil under a substantially constant cracking temperature and pressure both of Which are substantially uniform throughout the cracking system, which includes al heating Zone and an evaporating chamber, maintaining the entire body of oil in the system under the conditions of temperature and :pressure of the cracking reaction, maintaining upon the oil in the heating zone a pressure of not less than ten pounds in excess of the pressure upon the oil in the evaporating chamber, and substantially confining the cracking reaction to the evaporating chamber, by forcibly circula-ting the oil from the evaporating chamber to and through the heating Zone and back to the evaporating chamber at such a relation of speed and volume of circulation as to maintain such circulation equal to passing such entire body of oil through the heating Zone at intervals of not substantially more than ten minutes whereby such constant tempera-ture and pressure is maintained throughout the system.

4f. ln a cyclic process of cracking petroleum oil in a closed circulating system under a substantially constant cracking temperature and pressure, both of which are substantially uniform throughoutl the cracking system, including a heating @one and an evaporating chamber, maintaining -a relatively large body of oil in the evaporating chamber and circulating a relatively small stream thereof to and through the heating Zone and back into said chamber, to produce a substantially uniform cracking reaction in said chamber during the entire run and to substantially confine the cracking reaction to the evaporating chamber'by forcibly circulating the oil from the evaporating chamber to and through the heating Zone and back to the evaporating chamber at such a relation of speed and volume of circulation as to maintain such circulation equal to passing such entire body of oil through the heating Zone at intervals of not substantially more than ten minutes, and maintaining, during the entire run, all portions of such oil at so nearly the same temperature that the teinperature of the oil at its eXit from the heating Zone is less than 15 F. above the teniperature of the oil in said chamber, whereby such constant temperature and pressure is maintained throughout the system. i

5. A continuous cyclic cracking process,

consisting in primarily he-ating a. moving body of petroleum oil having a material range of boiling points to a temperature above then passing such heated liquid into a circuy latory cracking system proper, which includes a heating zone and evaporating chamber, in which chamber a relatively large body of oil is maintained, maintaining such oil at a substantially constant cracking temperature and pressure substantially uniform throughout the circulating system of said heating zone and chamber during the entire run by forcibly circulating a relatively small stream thereof from the evaporating chamber to and through the heating zone at such a relation of speed and volume of circulation as to maintain such circulation equal to passing the entire body of oil through the heating Zone at intervals of not more than ten minutes, and maintaining, during the entire run, all portions of such oil at so nearly the same temperature that theI temerature of the oil at its exit from the heating zone is less than 15C F. above the temperature of the oil in said chamber whereby the cra-cking reaction is substantially confined to said chamber.

6. A continuous cyclic cracking process, consisting in primarily heating a moving body of petroleum oil having a material range of boiling points to a temperature above the boiling point of a fraction or fractions thereof while subjecting the same to a pressure sufficient to maintain the same in substantially liquid form, in which primary heating the oil is brought approximately to the active cracking reaction temperature of the higher boiling point fractions of the oil, a material portion of the heat necessary to raise the oil to such temperature being supplied by heating means independent of the heating means. of 'the cracking system proper, then passing such heated liquid into a cyclic cracking system proper, including a 'heating Zone and an evaporating chamber wherein the entire body of oil in such system is maintained under substantially constant conditions of cracking temperature and pressure and the cracking thereof substantially confined to the evaporating chamber, by forcibly circulating the oil from the evaporating chamber at such a relation of speed and volume of circulation as to maintain such circulation equal to passing such entire body of oil through the heating zone at intervals of not substantially more than ten minutes whereby such constant temperalll@ ian

ture and pressure is maintained throughoutthe system Without subjecting any portion of the oil to excessive local temperature so that resultant excessive cracking and carbon deposit in any portion of the heatingv zone is avoided.

7. The cyclic procss of cracking petroleum oil which consists in primarily heating the oil to approximate-ly the temperature of the cracking reaction, continuously feeding the primarily heated oil into a closed cyclic cracking system proper, including a heating zone and an evaporating chamber, maintained at a substantially constant cracking temperature and pressure both of which are substantially uniform throughout the cracking system, maintaining a relatively large body of oil in the evapo-rating chamber and forcibly circulating a relatively small stream thereof therefrom through the heating zone and back into the chamber at such a relation of speed and volu-mel of circulation as to maintain. such clrculation equal to passlng such entire body through the heating zone at intervals of not substantially more than ten minutes whereby said constant temperature and pressure are maintained, continuously withdrawing the low boiling point vapor as produced and continuously discharging from the system high boiling points RICHARD lV. HAXNA. WILLIAM D. MASON. 'WALTER G. HAMILTON.

Witnesses:

FREDERICK S. LYON, nCHESTER E. SINGER. 

